Automatic telephone-exchange systems



March 22, 1955 B. B. JOHNSON 2,704,785

AUTOMATIC TELEPHONE-EXCHANGE SYSTEMS 3 Sheets-Sheet l Filed May 1, 195o z Uf 525% j/jf. ifa) March 22, 1955 B, B, JOHNSON 2,704,786

AUTOMATIC' TELEPHONE-EXCHANGE SYSTEMS Filed may 1, 195o s sheets-sheet 2 f4 7a) L 6 510 /5 fa March 22, 1955 B,

B. JOHNSON 2,704,786

AUTOMATIC TELEPHONE-EXCHANGE SYSTEMS Filed May l. 1950 3 Sheets-Sheet 5 l fa) fs f/a W m 19 z2@ United States Patent O AUTOMATIC TELEPHONE-EXCHANGE SYSTEMS Benjamin Bertie Johnson, Streatham, London, England,

assignor to Telephone Manufacturing Company Limited, Loudon, England, a company of Great Britain Application May 1, 1950, Serial No. 159,322

Claims priority, application Great Britain May 2, 1949 6 Claims. (Cl. 179-18) This invention relates to automatic telephone-exchange systems (the Word telephone being used in a non-limiting sense).

The invention provides an improved pre-selector stage, in which the switching of subscribers lines to a succeeding stage, usually a selector stage, is effected by relay devices, hereinafter referred to as selective relay units.

A selective relay unit may be said to consist of an electro-magnetic relay having a plurality of banks of contacts with means for determining which bank of contacts shall be operated upon by the relay armature when its operating electro-magnet is energized. It differs from the corresponding part of a so-called crossbar switch in that selection of a bank of contacts, instead of being effected by a bar, one of a number extending across a number of units, is effected by a finger magnet, one of a number individual to the unit, and associated one with each bank of contacts.

According to the present invention in its broadest aspect, an automatic telecommunication switching system for connecting lines of one order to lines of another order is characterized in that a preselector is associated with each line of one order, said preselector comprising a selective relay unit consisting of an electro-magnetic relay having a plurality of banks of contacts with a number of finger magnets one associated with each bank of contacts for determining which bank of contacts shall be operated upon by the relay armature when its operating electro-magnet is energized.

In one arrangement an automatic telecommunication system includes at least one trunk provided with a pre-selector for giving any one of a plurality of subscribers lines access to the said trunk if free to the exclusion of all others, characterized in that the preselector is a selective relay unit of the type referred to.

According to the present invention in a more restricted aspect, an automatic telecommunication switching system includes a plurality of trunks each provided with a preselector for giving any one of a plurality of subscribers lines access to the trunk with which it is associated if free to the exclusion of all others, characterized in that each preselector is a selective relay unit of the type referred to.

In either aspect of the invention each subscribers line may be served by a single bank of contacts with its associated finger magnet in the (or in each) selective relay unit and said system may be provided with means operated upon the initiation of a call over said line for energizing the said linger magnet and for preventing the energization of any other :finger magnet in the (or in any of the) selective relay units by any other subscriber during the process of establishing a connection between the said subscribers line and the trunk (or one of the trunks).

Alternatively, in either aspect of the invention two subscribers lines may be served by a single bank of contacts with its associated finger magnet in the (or in each) selective relay unit and said system may be provided with means operated upon the initiation of a call over either of said two lines for energizing said linger magnet and for preventing the energization of any other finger magnet in the or any of the selective relay units during the process of establishing a connection between the said subscribers line and the trunk (or one of the trunks). In this alternative trunk ar- 2,704,786 Patented Mar. 22, 1955 Frice rangement, since two subscribers lines are served by a single bank of contacts and its associated finger magnet which may be operated in response to a call over either of the two subscribers lines, the trunk (or each trunk) is provided with a switching means operated in dependence upon over which of the two subscribers lines the call is initiated for determining which of the two subscribers lines shall be effectively connected t0 the trunk.

In either embodiment of the invention, the trunk (or each trunk) may be provided with preferably two, though there may be more than two, selective relay units of the type referred to, each serving to give any one of a plurality of subscribers lines access to the trunk with which it is associated if free to the eX- clusion of all others the pluralities of subscribers lines served by the two selective relay units, being different and including means controlled in accordance with the line over which a call is initiated for determining which of the two selective relay units is to operate to effect the connection between the said line and the trunk concerned.

A brief description of the manner in which the preselector stage embodying the invention operates wiil be given, reference being made to the accompanying drawing in three parts numbered, respectively Figure 1(11), Figure l(b), and Figure 1(0); (these should be placed and read together in alignment in that order with Figure 1(a), on the left); and

Fig. 2 which shows a schematic diagram of the arrangement of the linger magnet circuits in the system of my invention.

lt will be assumed, for the purpose of the following description that there are a plurality of trunks, that each trunk is provided with one preselector comprising two selective relay units each having five banks of contacts, and that each bank of contacts with its single finger magnet, serves two subscribers lines.

Two selective relays per trunk, with five banks of contacts per unit, and two lines per bank gives each trunk access to twenty lines.

The drawing shows in a conventional manner, one preselector with its two selective relay units for giving any one of twenty subscribers lines access to the trunk leading to an A and B feed which it serves, and one subscribers line.

Before a description of the circuit be given, some reference to the conventions used in the drawing should be made. The drawings follow the analytic method. ln Figure l(b) there are shown two columns of contacts. The left-hand column comprises all the contacts belonging to one of the selective relay units, and the right hand column comprises all the contacts belonging to the other of the two selective relay units, associated with the trunk leading to an A and B feed. The operating magnets for these two selective relay units are shown in Figure l(a), and are given references BMI and BM11 respectively. Physically they would be associated with the two columns of contacts.

Each column of contacts comprises six rows of contacts, and the thickened lines represent contacts which are common or connected together.

lf one of the columns is considered, say the left-hand one, it will be seen that the top row has two contacts numbered respectively 1 and S. These are the first and last of five contacts: that is, between these two contacts there would be three other similar contacts, numbers 2, 3, and 4. They are omitted from the drawing so as not to complicate it. The five contacts in the top row of the left-hand column are connected to the negative conductor of subscribers lines 1 to 5 (assuming a straight distribution). The second row down comprises similar five contacts of which 6 and 0 are shown. The five contacts in this second row of contacts of the left-hand column are connected to the negative conductors of subscribers lines 6 to 9 and 0. The third, fourth, fifth and sixth rows of contacts are exactly similar to the first and second, the contacts in the third row being connected to the positive conductors of subscribers lines 1 to 5, those in the fourth to the positive conductor of subscribers lines 6 to 9 and 0, those in the fifth row to the test or private conductors for subscribers lines 1 to 5 and those in the sixth row to the test or private wires of subscribers lines 6 to 9 and l). The right-hand column of contacts is exactly similar to the left-hand column, but the contacts are connected to the respective conductors of subscribers lines 11 to 15 and 16 to 19 and 1G.

It will be seen from what has already been said, that each column of contacts comprises five minor columns of contacts, and that the contacts in each minor column of contacts have connected to them the negative, positive and private wires of two subscribers lines.

Associated with the five minor columns of contacts in the left-hand column of contacts are five finger magnets and five fingers f1, f10, one finger magnet and one finger for each minor column. A finger is a member which, when the finger magnet with which it is associated is energized, is interposed between the bottom of the minor column of contacts which it serves, and the armature arl, ar2, of the selective relay unit. A finger magnet is an electro-magnet which operates upon a single finger for interposing said finger between the bank of contacts with which it is associated and the armature of the selective relay unit.

Similarly, five finger magnets and fingers are associated with the right-hand column of contacts.

In Fig. 1(11) are shown two symbols marked FM. Each of these symbols marked FM represents ten nger magnets (assuming that there are ten trunks leading to A and B feeds serving one group of subscribers lines). Each finger magnet has a single finger. Thus considering the upper symbol marked FM, one of the ten finger magnets which it symbolizes is associated with the left-hand minor column of contacts in the left-hand column of the preselector illustrated in Fig. l; (a), (b), (c) the other nine finger magnets are associated with minor columns of contacts in nine other preselectors serving the same subscribers lines. The manner in which the finger magnets for the first, second, third, fourth, and fifth minor columns are connected is shown in Fig. 2, in which each square represents a single finger magnet and the multipling by which the other nine are connected. Thus, the upper five finger magnets FM1 FMS in Fig. 2 control fingers fl, f2, f3, f4 and f5 which serve the minor columns in the left-hand selective relay unit shown in Fig. l(b). The lower five finger magnets FM6 FM9 and PM10 control fingers f6, f7, f8, f9 and f1() which serve the minor columns of the right-hand selective relay unit.

As with most automatic telephone (and analogous switching systems) and as with most systems involving a number of relays, it is most convenient to describe the system of the present invention in terms of establishing a connection between a calling subscriber and the trunk leading to the A and B feed, and this I shall now proceed to do. I will assume that it is No. l subscriber who is calling.

When subscriber No. l initiates a call an obvious circuit is closed for relay L. Relay L at its contact l1 (line 1) closes a circuit for relay STA in series with the ten finger magnets (one for each of the ten preselectors which serves his line) symbolized by the upper FM in Fig. l(a). lt also at this same contact opens the circuit between relay STA and all the other groups of ten finger magnets as can be seen from Fig. 2.

The ten finger magnets symbolized by the upper FM in Fig. 1(a), are energized in this circuit and each interposes its finger between the left-hand minor column in the left-hand column of its associated preselector. Nothing results from this operation yet.

Relay STA is the start-relay for subscribers 1 to 5 and when it operates, it, at contacts stal, sta2 and staf, opens the circuits for relays STB, STC and STD, which are the start relays for subscribers 6 to 9 and 0, 11 to 15, and 16 to 19 and 10 respectively. (lt will be seen that each of these relays is able, when operated, to disable the other three.) Thus, until the line relay L of subscriber 1 is released, either as a result of the establishment of a connection to the trunk leading to the A and B feed or because he hangs up his telephone no other subscriber can interfere with the operations initiated.

At contact staS obvious circuits are completed for relays ST and STX which are start relays for a trunk searcher comprising relays SSA to SSE and `SSF to SSI,

of these only SSA, SSB and SSI are shown, the place where the others would be connected being indicated at X.

Relay ST, at its contacts stl to st5 connects the test wires of five of the ten trunks leading to A and B feeds which can serve subscriber 1 to relays SSA SSE, and relay STX at its contacts stxl to stx5 connects the test wires of the other five trunks to relays SSP` SSI.

It Will be assumed that the trunk shown in Fig. l (a), (b), (c) is available, that is that there is negative, through relay T, on test wire T. On this assumption, relays SSA and T will operate.

Relay SSA, at contacts ssal will disable relays SSB. SSI, at contacts ssa2 and ssa4 will connect by way of contacts sta4, the winding of selective relay unit bar magnet BM1 to the holding wire h of the trunk shown in Fig. 1, to which holding wire relay T has, by its contact t1 connected earth.

Magnet BM1 operates, and at its contact bm1 closes a holding circuit, to wire h, for itself. It also operates the contacts of the left-hand minor column in the lefthand column of contacts in the selective relay unit belonging to the trunk selected, that is, in the case under consideration, trunk 1. Thus the positive (-1-) and negative lines of the subscriber are, except for the break at contact k1, connected to -l-(a) and (a) conductors of the trunk and to the A relay (not shown) of that trunk. At the same time, relay K is connected by the selective relay unit to conductor P(a) where it finds earth and operates.

Relay K at its contacts k1 and k2, cuts the earth and line relay negative from the line so that line relay L releases and, so doing, releases relay STA and all other common relays which depended upon its operation.

As is common in relay selectors in the telephone art, when the subscriber is connected, by a preselector, to the A and B feed, the A relay in the A and B feed initiates operations which cause earth to be connected to the H (or holding) wire. The A and B feed is not shown in the accompanying drawings as it does not form part of the invention and may be of quite conventional design; it is represented by the rectangle to the right of Fig. l(c). The earth is connected to wire H before relay T, which is a retarded release relay, releases.

The calling subscriber was supposed to have been No. 1. Had the calling subscriber been No. 6, the same selective relay unit (that is the same magnet BM1) and the same minor column of contacts (that is the same finger magnet FM) would have been involved. In order that the trunk may differentiate, between the two, it is provided with a relay SW (Fig. 1(0)). The circuit for the finger magnets, in this case, includes relay STB instead of relay STA.

Relay STB brings about the same operations as did relay STA with the additional operation of closing a circuit over contact stb6, by way of contacts ssaS, for relay SW Fig. 1(0). Relay SW operates and holds itself to earth at contact t1 (later replaced by earth from the A and B feed) it also switches conductors -l-(b), (b) and P(b) instead of conductors -l-(a), (a) and P(a) to line relay A (not shown) of the trunk.

Had the call been initiated by subscriber No. 11, operations would have been of the same nature as for subscriber No. 1, except that the lower finger magnets FM (Fig. 1(a)) would have operated in series with relay STC, with the result that bar magnet BM11, instead of BM1 (see contacts stc4) would have operated.

Subscriber No. 16 would have caused relay STD to operate: operations would have been similar to those for subscriber No. 11, except that relay SW, Fig. 1(0), would have operated in a manner similar to that in which it operated for subscriber 6, contact std6 being involved.

Had the first trunk been unavailable, a condition which would have been indicated by the absence of earth in wire T, upon a subscriber in the group served by the trunk illustrated initiating a call, everything would have proceeded as for subscriber No. 1 up to the point at which relays ST and STX operated.

When relays ST and STX operate, they, as before, connect the test wires of all the trunks 1 to 10 of the group, to the relays SSA SSI. Because trunk 1 is unavailable relay SSA cannot operate, but if trunk 2 is available relay SSB can operate. The reason that relay SSA cannot operate is that the circuit of the T wire is open at contacts b1 or haS, these contacts being operated by relays (not shown) in the A and B feed. This is conventional. At contact ssbl (not shown) the circuit for all relays SSC SS] is opened so that they cannot operate. Relay SSB brings about the same operations for trunk 2 as relay SSA did for trunk 1.

Further extension of the connection, beyond the trunk to which I have described the subscribers line as being connected will depend upon the nature of the apparatus provided at the next stage, for example, whether it is a group selector, operators position, and so forth.

It is clear, that the selective relay units could be associated With the subscribers lines instead of with the trunks.

I claim:

1. An automatic telecommunication switching system including a plurality of trunks, a plurality of subscribers lines, a preselector for each trunk, each preselector for giving any one subscribers line access to said trunk if free, said preselector comprising an electro-magnetic relay having an armature, a plurality of banks of contacts, means connecting subscribers lines to said banks one to each, means connecting said trunk to all said banks, a iinger magnet associated With each bank, a single nger for each linger magnet, a line relay operated upon the initiation of a call over any subscribers line, a circuit including a contact of said line relay and said finger magnet said contact closing said circuit when said line relay is energized for energizing the finger magnet associated With its bank, a relay included in said circuit and having contacts for preventing the energization of any other finger magnet of said preselector during the process of establishing a connection between said subscribers line initiating said call and said trunk, means for interposing the finger of said energized linger magnet between the associated bank of contacts and the armature of said electro-magnetic relay, means for testing the free or engaged condition of said trunk, and means for energizing said electro-magnetic relay to operate the bank of contacts having said interposed finger if said trunk is free.

2. An automatic telecommunication system including at least one trunk, a plurality of subscribers lines grouped in pairs, a preselector for giving any one subscribers line access to said trunk if free, said preselector comprising an electro-magnetic relay having a plurality of banks of contacts, means connecting the lines of said pairs to different contacts in said banks, one pair to each bank, means connecting said trunk to contacts in all said banks, one nger magnet associated with each bank, a single finger for each ringer magnet, a line relay for each line of a pair operated upon the initiation of a call over said line of said pair, circuits each including a contact of one of said line relays, and said linger magnet either said contact closing its circuit when said line relay is energized for energizing the iinger magnet associated with the bank to which said pair of lines is connected, means for preventing the energization of any other nger magnet during the process of establishing a connection between said line initiating said call and said trunk, means for interposing the inger of said energized finger magnet between the associated bank of contacts and the armature of said electro-magnetic relay, means for energizing said electro-magnetic relay to operate the bank of contacts having said interposed nger, and means for completing the connection of either of the subscribers lines of a pair to its contacts in its bank of contacts.

3. An automatic telecommunication system as set forth in claim 2, including a changeover relay associated with said selector, irst connections between resting contacts of said changeover relay and contacts in all said banks of contacts to each of which one subscribers line of each pair is connected, second connections between make contacts of said changeover relay and contacts in all of said banks of contacts to each of which the other subscribers line of each pair is connected, means including line relays and auxiliary line relays operated upon the initiation of a call by any one of said other subscribers of said pairs energizing said changeover relay, said changeover relay when energized disconnecting said first connections from and connecting said connections to said trunk.

4. An automatic telecommunication system including at least one trunk, a plurality of subscribers lines, a pair of preselectors one connecting some of said subscribers lines to said trunk and the other connecting the others of said subscribers lines to said trunk, each said preselector comprising an electro-magnetic relay having a plurality of banks of contacts, a finger magnet for each bank of contacts, a nger for each ringer magnet, a line relay, a circuit including contacts of said line relay, means operating one nger magnet in one said preselector upon initiation of a call by any one of said subscribers lines, a relay in said circuit said relay having contacts for preventing energization of any other finger magnet in either of said preselectors during the process of establishing a connection between said one of said subscribers lines and said trunk, means for interposing the linger of the energized inger magnet between the associated bank of contacts and the armature of the electro-magnet having said bank of contacts, and means for energizing one of said electro-magnetic relays to operate the bank of contacts having said interposed nger.

5. An automatic telecommunication system including at least one trunk, a plurality of subscribers lines, at least one preselector for connecting any one of said subscribers lines to said trunk, said preselector comprising an electro-magnetic relay having a plurality of banks of contacts, a finger magnet associated with each bank of contacts, a finger for each linger magnet associated with one bank of contacts on said electro-magnetic relay, a line relay for each subscribers line, a circuit for each finger magnet said circuit including contacts of said line relays each said contact closing a circuit for one nger magnet and opening the circuits of all other nger magnets associated with any other bank of contacts on said electro-magnetic relay, circuit arrangements for simultaneously energizing other finger magnets associated with one bank of contacts on other electro-magnetic relays, a test circuit for said trunk, a test relay for said preselector for testing the free or engaged condition of said trunk, a circuit including contacts of said test relay for operating the first-mentioned electro-magnetic relay if said trunk is free to operate the bank of contacts having the interposed nger, and means for closing a circuit to another electro-magnetic relay if said trunk is engaged.

6. A system according to claim 5, including means for preventing simultaneous operation of iinger magnets on said other electro-magnetic relays except said other finger magnets associated with said one bank of contacts on said other electro-magnetic relays.

References Cited in the tile of this patent UNITED STATES PATENTS 1,529,419 Betulander Mar. 10, 1925 1,568,039 Williams Dec. 29, 1925 1,593,387 Clark July 20, 1926 2,039,644 Gleason et al May 5, 1936 2,310,634 Holden Feb. 9, 1943 2,324,624 Holden Iuly 20, 1943 2,326,551 Mohr Aug. 10, 1943 2,519,849 Ostline Aug. 22, 1950 

